/*
 * base64.cpp
 *
 *  Created on: 20.01.2020
 */

#include <stdint.h>
//#include <stdlib.h>

#include "base64.h"

namespace Base64 {
	namespace {
		char encoding_table[] = {
				'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
				'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
				'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
				'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
				'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
				'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
				'w', 'x', 'y', 'z', '0', '1', '2', '3',
				'4', '5', '6', '7', '8', '9', '+', '/'
		};

		int mod_table[] = {0, 2, 1};

		uint8_t decoding_table[256];
	}

	size_t getLengthEncode(size_t input_length) {
		return 4 * ((input_length + 2) / 3);
	}

	size_t getLengthDecode(size_t input_length) {
		return input_length / 4 * 3;;
	}

	size_t base64_encode(
			const unsigned char *data,
			unsigned char* encoded_data,
			size_t input_length,
			size_t buffersize) {

		size_t output_length = 4 * ((input_length + 2) / 3);

		if (output_length > buffersize)
			return 0;

		if (encoded_data == 0) {
			return 0;
		}

		for (size_t i = 0, j = 0; i < input_length;) {

			uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0;
			uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0;
			uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0;

			uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

			encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
			encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
			encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
			encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
		}

		for (int i = 0; i < mod_table[input_length % 3]; i++)
			encoded_data[output_length - 1 - i] = '=';

		return output_length;
	}


	size_t base64_decode(const char *data,
								 unsigned char* decoded_data,
								 size_t input_length,
								 size_t buffersize) {

		if (input_length % 4 != 0)
			return 0;

		size_t output_length = input_length / 4 * 3;

		if (output_length > buffersize)
			return 0;


		if (data[input_length - 1] == '=') (output_length)--;
		if (data[input_length - 2] == '=') (output_length)--;

		if (decoded_data == 0)
			return 0;


		for (size_t i = 0, j = 0; i < input_length;) {

			uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[(uint8_t) data[i++]];
			uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[(uint8_t) data[i++]];
			uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[(uint8_t) data[i++]];
			uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[(uint8_t) data[i++]];

			uint32_t triple = (sextet_a << 3 * 6)
			+ (sextet_b << 2 * 6)
			+ (sextet_c << 1 * 6)
			+ (sextet_d << 0 * 6);

			if (j < output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
			if (j < output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
			if (j < output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
		}

		return output_length;
	}


	void init() {
		for (int i = 0; i < 64; i++)
			decoding_table[(unsigned char) encoding_table[i]] = i;
	}

}

